1. Field of the Invention
The present invention relates to an exhaust system connected to an internal combustion engine, and more particularly to a joint structure for connecting a plurality of exhaust pipes with each other.
2. Description of the Related Art
In general, an internal combustion engine is mounted swingably in order to avoid the transmission of much vibrations in operation to a chassis. A size and magnitude of vibrations of the internal combustion engine is determined by a mount position of the internal combustion engine in the chassis, a spring constant of the mount, and a torque reactive force to be applied to the internal combustion engine. Then, in general, a swing center axis of the internal combustion engine for a torque reactive force of the internal combustion engine is referred to as a roll axis.
In the case where an exhaust gas system is mounted in a vehicle such as an FF vehicle in which an internal combustion engine is mounted on a front portion of the chassis and the front wheels are driven and the torque reactive force is large so that the vibrations of the internal combustion engine are remarkable, the exhaust pipes are largely vibrated in accordance with the vibrations of the internal combustion engine when the vehicle is started and accelerated. For this reason, a joint is provided for moderating the force to be applied to the exhaust pipes due to the vibrations of the internal combustion engine and for interrupting the transmission of the vibrations.
By the way, in order to prevent the degradation of the exhaust gas efficiency of the internal combustion engine due to the exhaust gas interference, a so-called dual exhaust system is utilized. In such an exhaust system, two independent exhaust pipes are connected successively after the dual exhaust manifold connected to exhaust ports of the internal combustion engine.
Also, the above-described joint for interrupting the vibrations is provided in such a dual exhaust system.
For example, in Japanese Utility Model Application No. Hei 2-63025, as shown in FIG. 10, there have been proposed a joint for an exhaust pipe characterized in that a flange 101 having bolt holes for integrating the exhaust pipes in alignment with each other is formed at end portions of a plurality of exhaust pipes 100 connected to a body of an engine, a mounting flange 102 having bolt holes and connected to the above-described flange 101 is mounted on an exhaust pipe 105 on a tail side for connecting with the above described exhaust pipes 100, and the mount flange 102 and the flange 101 are fixed to each other through a seal portion 103 to connect the exhaust pipes with each other. The publication discloses an embodiment in which the flange 101 is made in a spherical shape. Then, the publication discloses that if the flange 101 on the engine side and the mounting flange 102 are firmly fixed to each other by the bolts, the exhaust pipes on the engine side and the exhaust pipes on the tail side may be positively connected with each other in a slidable manner. Accordingly, even if the vibrations are transmitted from the engine to the exhaust pipes, the exhaust pipes located upstream and downstream of the joint are slidingly moved relative to each other along the seal surface of the seal member. The width of the movement is just allowed within a thickness of the seal portion 103 and a gap of the bolt holes.
By the way, when the internal combustion engine is fluctuated, the vibrations due to its fluctuation are transmitted to the exhaust pipes, so that the load caused by the vibrations is applied to the joint portion.
Also, in many cases, the arrangement of the joint is remote from the internal combustion engine. In the case where the internal combustion engine is fluctuated, there is a possibility that the two exhaust pipes in the dual exhaust system would be different from each other in directional shift amount, so that a strain might be generated between the two exhaust pipes.
Accordingly, in the case where the slidable direction of the joint is different from the load application direction or the direction of the strain, there is a fear that the joint per se would be damaged, or the joint portion would be lifted to open to allow the leakage of the exhaust gas.
Accordingly, it is desirable that, as in a single ball joint, a joint that is movable in all directions about one center for coping with universal-directional loads.
It is possible to provide such a joint that is movable about one center point by making the flanges spherical ones and causing the respective spherical shapes to have a common center point in the system disclosed in the above-described Japanese Utility Model Application No. Hei 2-63025. However, as a result, it is necessary to curve the exhaust pipes considerably to the outside at the flange portion. Thus, this approach involves a problem that the structure of the joint portion is enlarged in size. Also, in Japanese Utility Model Application No. Sho 61-84122 that corresponds to U.S. patent application Ser. No. 735,462, since the dual exhaust pipes are connected with each other with one ball joint so as to incorporate therein the two exhaust pipes, it is inevitable to enlarge the joint structure in the same way as in the foregoing approach.